List of alternative nonmetal classes

Metalloid	Unclassified nonmetal	Nonmetal halogen	Noble gas
B, Si, Ge, As, Sb, Te	H, C, N, P, O, S, Se	F, Cl, Br, I	He, Ne, Ar, Kr, Xe, Rn
Boron	Oxygen	Bromine	Krypton

In chemistry, after nonmetallic elements such as silicon, chlorine, and helium are classed as either metalloids, halogens, or noble gases, the remaining unclassified elements are H, C, N, O, P, S and selenium.

The nonmetallic elements are sometimes instead divided into three to five alternative classes according to, for example, electronegativity; the relative homogeneity of the halogens; molecular structure; the peculiar nature of hydrogen; the corrosive nature of oxygen and the halogens; and variations thereupon.

Two classes

Examples have author labels for convenience rather than precedence

Reactive nonmetal	Noble gas
H, C, N, P, O, S, Se, F, Cl, Br, I	He, Ne, Ar, Kr, Xe, Rn

Rudakiya. The nonmetals are simply classified according to their inclination to form chemical compounds. The halogens are not distinguished.

Three classes

Electronegative nonmetal	Very electronegative nonmetal	Noble gas
H, C, P, S, Se, I	N, O, F, Cl, Br	He, Ne, Ar, Kr, Xe, Rn

Wulfsberg. The nonmetals are divided based on a loose correlation between electronegativity and oxidizing power. Very electronegative nonmetals have electronegativity values over 2.8; electronegative nonmetals have values of 1.9 to 2.8.

Other nonmetal	Halogen	Noble gas
H, C, N, P, O, S, (Se)	F, Cl, Br, I, At	He, Ne, Ar, Kr, Xe, Rn

Gargaud et al. The halogens are in a class of their own; astatine is classified as a nonmetal; and the remaining nonmetals are referred to as other nonmetals. If selenium is counted as a metalloid rather than another nonmetal, the resulting set of less active nonmetals (H, C, N, P, O, S) are sometimes instead referred as organogens, CHONPS elements or biogens. Collectively these six nonmetals comprise the bulk of life on Earth; a rough estimate of the composition of the biosphere is C₁₄₅₀H₃₀₀₀O₁₄₅₀N₁₅P₁S₁.

Polyatomic element	Diatomic element		Monatomic element (noble gas)
C, P, S, Se	H, N, O, F, Cl, Br, I		He, Ne, Ar, Kr, Xe, Rn

Bettelheim et al. The nonmetals are distinguished based on the molecular structures of their most thermodynamically stable forms in ambient conditions. Polyatomic nonmetals form structures or molecules in which each atom has two or three nearest neighbours (C_x, P₄, S₈, Se_x); diatomic nonmetals form molecules in which each atom has one nearest neighbour (H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂); and the monatomic noble gases exist as isolated atoms (He, Ne, Ar, Kr, Xe, Rn) with no fixed nearest neighbour. This gradual reduction in the number of nearest neighbours corresponds (approximately) to a reduction in metallic character. A similar progression is seem among the metals. Metallic bonding tends to involve close-packed centrosymmetric structures with a high number of nearest neighbours. Post-transition metals and metalloids, sandwiched between the true metals and the nonmetals, tend to have more complex structures with an intermediate number of nearest neighbours

Four classes

Hydrogen	Nonmetal	Halogen	Noble gas
H	C, N, P, O, S, Se	F, Cl, Br, I, At	He, Ne, Ar, Kr, Xe, Rn

Field & Gray. Hydrogen is placed by itself on account of it being "so different from all other elements". The remaining nonmetals are divided into nonmetals, halogens, and noble gases, with the unnamed class being distinguished by including nonmetals with relatively strong interatomic bonding, and the metalloids being effectively treated as a third super-class alongside metals and nonmetals.

Hydrogen	Carbon and other nonmetals	Halogen	Noble gas
H	C, N, P, O, S, Se	F, Cl, Br, I, At	He, Ne, Ar, Kr, Xe, Rn

Dinwiddle. A variant of Field & Gray in which C, N, O, P, S, Se are classified as carbon and other nonmetals.

Metalloid	Intermediate nonmetal	Corrosive nonmetal	Noble gas
B, Si, Ge, As, Sb, Te	H, C, N, P, S, Se	O, F, Cl, Br, I, At	He, Ne, Ar, Kr, Xe, Rn

Vernon. The nonmetals are divided into four classes that complement a four-fold division of the metals, with the noble metals treated as a subset of the transition metals. The metalloids are treated as chemically weak nonmetals, in a manner analogous to their chemically weak frontier metal counterparts.

Five classes

Boroid	Organogen	Sulphuroid	Chloroid	Noble gas
B, Si	H, C, N, O	P, S, Se	F, Cl, Br, I	Not then known

Dupasquier. Noble gases were not yet known. H, C, N and O were grouped together on account of their occurrence in living things. P, S and Se were characterised as being solid; volatile at an average temperature between 100 degrees and red heat; and combustible and flammable.

Hydrogen	Semiconductor	Other nonmetal	Halogen	Noble gas
H	B, Si, Ge, As, Sb, Te	C, N, P, O, S, Se	F, Cl, Br, I, At	He, Ne, Ar, Kr, Xe, Rn

Myers et al. Metalloids are labeled as semiconductors and C, N, O, P, S, Se classified as other nonmetals.

Hydrogen	Metalloid	Nonmetal	Halogen	Noble gas
H	B, Si, Ge, As, Sb, Te, Po	C, N, P, O, S, Se	F, Cl, Br, I, At	He, Ne, Ar, Kr, Xe, Rn

Dingle. Hydrogen is again placed by itself on account of its uniqueness. The remaining nonmetals are divided into metalloids, nonmetals, (referred to as "quintessential nonmetals"), halogens, and noble gases. Since the metalloids abut the post-transition or "poor" metals, they might be renamed as "poor non-metals".

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